Method for producing nickel-containing hydroxide

ABSTRACT

A method for producing a nickel-containing hydroxide is provided that includes a particle growth step of promoting growth of nickel-containing hydroxide particles by neutralization crystallization in an aqueous solution accommodated in an agitation tank. In the particle growth step, an averaged value of the maximum accelerations of the flows of streamlines for the aqueous solution is greater than 600 m/s2.

TECHNICAL FIELD

The present invention relates to a method for producing anickel-containing hydroxide that is used as a precursor of the positiveelectrode active material of a lithium ion secondary battery.

BACKGROUND ART

In recent years, with the widespread use of portable electronic devices,such as mobile phones and notebook computers, there is a high demand forthe development of small and light nonaqueous electrolyte secondarybatteries having high energy density. There is also a high demand forthe development of high-output secondary batteries as batteries forelectric vehicles such as hybrid electric vehicles. Lithium ionbatteries are nonaqueous secondary batteries that can satisfy thesedemands. A lithium ion secondary battery includes a negative electrode,a positive electrode, an electrolyte solution, and the like. Materialscapable of sustaining lithium insertion and deinsertion are used as anegative-electrode active material and a positive electrode activematerial.

Lithium composite oxides, particularly, lithium-cobalt composite oxides,which are relatively easy to synthesize, are promising materials for useas the positive electrode material because lithium ion secondarybatteries that use lithium composite oxides as the positive electrodematerial can achieve a high voltage of around 4V. As such, practicalapplications of lithium ion secondary batteries using lithium compositeoxides are being developed as batteries having high energy density. Notethat numerous efforts have been made to develop lithium ion secondarybatteries using lithium-cobalt composite oxides with improved initialcapacity characteristics and cycle characteristics, and various positiveoutcomes have been obtained therefrom.

However, because an expensive cobalt compound is used as a raw materialin a lithium-cobalt composite oxide, the cost per capacity of batteriesusing lithium-cobalt composite oxides is substantially higher thannickel-hydrogen batteries, and as such, their applications aresubstantially limited. Thus, cost reduction of the positive electrodeactive material is desired with respect to both small secondarybatteries used in portable devices and large secondary batteries forelectric power storage and electric vehicles, and the development oftechniques for reducing the cost of the positive electrode activematerial to enable production of a more inexpensive lithium ionsecondary battery will have great potential and industrial significance.

An example of a potential new material to be used as the active materialof a lithium ion secondary battery includes a lithium-nickel compositeoxide that uses nickel, which is a cheaper alternative to cobalt. Thelithium-nickel composite oxide exhibits a lower electrochemicalpotential as compared with the lithium-cobalt composite oxide, and assuch, the lithium-nickel composite oxide may be less prone to problemsof decomposition due to oxidation of the electrolyte, achieve highercapacity, and exhibit a high battery voltage comparable to that of thecobalt-based lithium ion secondary battery. As such, active research anddevelopment efforts are being made with respect to the lithium-nickelcomposite oxide. However, when a purely nickel-based lithium compositeoxide synthesized with only nickel is used as the positive electrodeactive material of a lithium ion secondary battery, cyclecharacteristics may be degraded as compared with cobalt-based lithiumion secondary batteries. Also, such a purely-nickel-based lithium ionsecondary battery may be prone to battery performance degradation whenstored or used in a high temperature environment. In this respect,lithium-nickel composite oxides obtained by substituting a part ofnickel with cobalt or aluminum are generally known.

A general method for producing the positive electrode active materialinvolves (1) first, preparing a nickel composite hydroxide as aprecursor of the lithium-nickel composite oxide using the so-calledneutralization crystallization method, and (2) mixing the precursor witha lithium compound and firing the mixture. Of the above process steps, arepresentative example of process step (1) for producing particles bythe neutralization crystallization method includes a process using anagitation tank.

Patent Document 1 describes how the shear force generated by agitationaffects the growth of nickel hydroxide particles and how the averageparticle diameter of the nickel hydroxide particles decreases as theshear force gets stronger such that an impeller for controlling theshear force is necessary.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Publication No. 2003-2665

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Various studies have been conducted to produce nickel-containinghydroxide particles having desired characteristics.

However, production conditions have to be set up each time the type ordiameter of the impeller, the volume of the agitation tank, or someother structural change is made to the agitation apparatus.

Also, particles that have grown into spherical shapes may aggregate suchthat the sphericity of the particles obtained at the completion ofneutralization crystallization may be compromised, and such sphericitydegradation of the particles may adversely affect the characteristics ofthe lithium ion secondary battery.

The present invention has been made in view of the above problems of therelated art, and it is an object of the present invention to provide amethod for producing a nickel-containing hydroxide that can universallyprevent sphericity degradation of particles obtained at the completionof neutralization crystallization in various chemical reactionapparatuses having various structures.

Means for Solving the Problem

According to one embodiment of the present invention, a method forproducing a nickel-containing hydroxide is provided that includes aparticle growth step of promoting growth of nickel-containing hydroxideparticles by neutralization crystallization in an aqueous solutionaccommodated in an agitation tank. In the particle growth step, anaveraged value of the maximum accelerations of the flows of streamlinesfor the aqueous solution is greater than 600 m/s².

Advantageous Effect of the Invention

According to an aspect of the present invention, a method for producinga nickel-containing hydroxide may be provided that can universallyprevent sphericity degradation of particles obtained at the completionof neutralization crystallization in various chemical reactionapparatuses having various structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a method for producing a nickel-containinghydroxide according to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view of an aggregate formed duringa first half of a particle growth step according an embodiment of thepresent invention;

FIG. 3 is a schematic cross-sectional view of an outer shell formedduring a second half of the particle growth step according to anembodiment of the present invention;

FIG. 4 is a top view of a chemical reaction apparatus used to implementthe method for producing a nickel-containing hydroxide according to anembodiment of the present invention;

FIG. 5 is a cross-sectional view of the chemical reaction apparatusacross line V-V of FIG. 4;

FIG. 6 is a cross-sectional view of a circular horizontal plane arrangeddirectly above an impeller and streamlines passing through thehorizontal plane from the top to bottom according to an embodiment ofthe present invention;

FIG. 7 is an SEM image of nickel composite hydroxide particles obtainedin Example 1; and

FIG. 8 is an SEM image of nickel composite hydroxide particles obtainedin Comparative Example 1.

EMBODIMENTS FOR IMPLEMENTING THE INVENTION

In the following, embodiments of the present invention will be describedwith reference to the accompanying drawings. Note that in the presentdescription and the drawings, identical or corresponding elements aregiven the same reference numerals and overlapping descriptions thereofmay be omitted.

FIG. 1 is a flowchart showing a method for producing a nickel-containinghydroxide according to an embodiment of the present invention. Themethod for producing a nickel-containing hydroxide shown in FIG. 1 is amethod for obtaining nickel-containing hydroxide particles byneutralization crystallization, and includes a nucleation step S11 forgenerating nuclei of particles and a particle growth step S12 forpromoting growth of the particles. Each of the above steps will bedescribed below after describing the nickel-containing hydroxide to beobtained.

(Nickel-Containing Hydroxide)

The nickel-containing hydroxide is used as a precursor of thepositive-electrode active material of a lithium ion secondary battery.The nickel-containing hydroxide may be (1) a nickel composite hydroxidethat contains nickel (Ni), cobalt (Co), and aluminum (Al) at an amountratio (mole ratio) of Ni:Co:Al=(1-x-y):x:y (where 0≤x≤0.3,0.005≤y≤0.15), or (2) a nickel-cobalt-manganese composite hydroxide thatcontains nickel (Ni), cobalt (Co), and manganese (Mn), and element M(where M denotes at least one additional element selected from a groupconsisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) at an amount ratio(mole ratio) of Ni:Co:Mn:M=x:y:z:t (where x+y+z+t=1, 0.1≤x≤0.7,0.1≤y≤0.5, 0.1≤z≤0.8, 0≤t≤0.02), for example.

The amount of hydroxide ions included in a nickel-containing hydroxideaccording to one embodiment may normally have a stoichiometric ratio,but the amount of hydroxide ions may be excessive or deficient to theextent that no substantial influence is cast on the present embodiment.Also, a part of the hydroxide ions may be replaced with anions (e.g.,carbonate ions, sulfate ions, etc.) to the extent that no substantialinfluence is cast on the present embodiment.

The hydroxide according to one embodiment may be any single phase of anickel-containing hydroxide (or substance primarily containing anickel-containing hydroxide) as measured by X-ray diffraction (XRD).

The nickel-containing hydroxide contains nickel, and preferably furthercontains a metal other than nickel. A nickel-containing hydroxidefurther containing a metal other than nickel will be referred to as anickel composite hydroxide. Because the metal composition ratio of thenickel composite hydroxide (e.g., Ni:Co:Mn:M) will be maintained even inthe positive electrode active material to be obtained, the metalcomposition ratio of the nickel composite hydroxide is preferablyadjusted to match the desired metal composition ratio of the positiveelectrode active material.

(Method for Producing Nickel-Containing Hydroxide)

As described above, the method for producing a nickel-containinghydroxide includes a nucleation step S11 and a particle growth step S12.In the present embodiment, the nucleation step S11 and the particlegrowth step S12 are carried out separately by using a batch agitationtank and controlling the pH value of the aqueous solution in theagitation tank, for example.

In the nucleation step S11, nucleation takes precedence over particlegrowth and particle growth hardly occurs. On the other hand, in theparticle growth step S12, particle growth takes precedence overnucleation and new nuclei are hardly generated. By performing thenucleation step S11 and the particle growth step S12 separately,homogenous nuclei with a narrow particle size distribution range may beformed, and the nuclei may be homogenously grown thereafter.

In the following, the nucleation step S11 and the particle growth stepS12 will be described. Note that the pH value range of the aqueoussolution in the agitation tank during the nucleation step S11 and the pHvalue range of the aqueous solution in the agitation tank during theparticle growth step S12 are different, but the ammonia concentrationrange and the temperature range of the aqueous solution may besubstantially the same.

Note that although a batch agitation tank is used in the presentembodiment, a continuous agitation tank may be used as well. When acontinuous agitation tank is used, the nucleation step S11 and theparticle growth step S12 are carried out at the same time. In this case,the pH value range of the aqueous solution in the agitation tank willnaturally be the same and may be in a range around 12.0, for example.

(Nucleation Step)

First, a raw material liquid is prepared. The raw material liquidcontains at least a nickel salt, and preferably further contains a metalsalt other than the nickel salt. The metal salt may be a nitrate, asulfate, a hydrochloride, or the like. More specifically, for example,nickel sulfate, manganese sulfate, cobalt sulfate, aluminum sulfate,titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate,vanadium sulfate, ammonium vanadate, chromium sulfate, potassiumchromate, zirconium sulfate, zirconium nitrate, niobium oxalate,ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate,ammonium tungstate, and the like may be used as the metal salt.

Because the metal composition ratio of the raw material liquid (e.g.,Ni:Co:Mn:M) is maintained even in the nickel composite hydroxide to beobtained, the metal composition ratio of the raw material liquid isadjusted to match the desired metal composition ratio of the nickelcomposite hydroxide.

Also, an aqueous solution obtained by supplying and mixing an alkalineaqueous solution, an aqueous ammonia solution, and water is stored in anagitation tank. The mixed aqueous solution is hereinafter referred to as“pre-reaction aqueous solution”. The pH value of the pre-reactionaqueous solution is adjusted to be within the range from 12.0 to 14.0,and preferably within the range from 12.3 to 13.5, at a liquidtemperature of 25° C. as the reference temperature. Also, theconcentration of ammonia in the pre-reaction aqueous solution ispreferably adjusted to be within the range from 3 g/L to 25 g/L, morepreferably within the range from 5 g/L to 20 g/L, and more preferablywithin the range from 5 g/L to 15 g/L. Further, the temperature of thepre-reaction aqueous solution is preferably adjusted to be within therange from 20° C. to 60° C., and more preferably within the range from35° C. to 60° C.

The alkaline aqueous solution may be an aqueous solution containing analkali metal hydroxide such as sodium hydroxide, potassium hydroxide, orthe like. The alkali metal hydroxide may be supplied as a solid but ispreferably supplied as an aqueous solution.

The ammonia aqueous solution may be an aqueous solution containing anammonia supplier. The ammonia supplier may be, for example, ammonia,ammonium sulfate, ammonium chloride, ammonium carbonate, ammoniumfluoride, or the like.

Note that in the present embodiment, an ammonia supplier is used as anon-reducing complexing agent. However, in other embodiments,ethylenediaminetetraacetic acid, nitrito triacetic acid, uracil diaceticacid, glycine, or the like may be used, for example. That is, anynon-reducing complexing agent that is capable of bonding with a nickelion or the like to form a complex in an aqueous solution accommodated inan agitation tank may be used.

After adjusting the pH value, the ammonia concentration, thetemperature, and the like of the pre-reaction aqueous solution, the rawmaterial liquid is supplied into the agitation tank while agitating thepre-reaction aqueous solution. In this way, the pre-reaction aqueoussolution and the raw material liquid may be mixed together to form areaction aqueous solution in the agitation tank, and the nucleation stepS11 of generating nuclei by neutralization crystallization may bestarted.

In the nucleation step S11, when the pH value of the reaction aqueoussolution is greater than or equal to 12.0, nucleation takes precedenceover particle growth. Also, in the nucleation step S11, when the pHvalue of the reaction aqueous solution is less than or equal to 14.0,the nuclei may be prevented from becoming too fine, and gelation of thereaction aqueous solution may be prevented. In the nucleation step S1,the fluctuation range (the range between the maximum value and theminimum value) of the pH value of the reaction aqueous solution ispreferably less than or equal to 0.4.

Also, in the nucleation step S11, when the ammonia concentration in thereaction aqueous solution is greater than or equal to 3 g/L, thesolubility of metal ions may be kept constant and generation of nucleiwith accurate shapes and particle diameters may be promoted. Also, inthe nucleation step S11, when the ammonia concentration in the reactionaqueous solution is less than or equal to 25 g/L, the amount of metalions remaining in the aqueous solution without precipitating may bereduced and production efficiency may be improved. In the nucleationstep S11, the fluctuation range (the range between the maximum value andthe minimum value) of the ammonia concentration of the reaction aqueoussolution is preferably less than or equal to 5 g/L.

Also, in the nucleation step S11, when the temperature of the reactionaqueous solution is greater than or equal to 20° C., thenickel-containing hydroxide may be substantially soluble in the reactionaqueous solution such that nucleation may be gradual and nucleation maybe easily controlled. Also, when the temperature of the reaction aqueoussolution is less than or equal to 60° C., volatilization of ammonia maybe prevented so that the amount of ammonia water used may be reduced andproduction costs may be reduced.

In the nucleation step S11, an alkaline aqueous solution and an ammoniaaqueous solution are supplied to the agitation tank in addition to theraw material liquid so that the pH value, the ammonia concentration, andthe temperature of the reaction aqueous solution can be maintainedwithin the above ranges. In this way, nucleation may be continued in thereaction aqueous solution. After a predetermined amount of nuclei aregenerated, the nucleation step S11 is ended. Note that whether thepredetermined amount of nuclei has been generated can be estimated basedon the amount of metal salt supplied.

(Particle Growth Step)

After completing the nucleation step S11 and before starting theparticle growth step S12, the pH value of the reaction aqueous solutionin the agitation tank is adjusted to be lower than the pH value of thereaction aqueous solution during the nucleation step S11 and is adjustedto be within the range from 10.5 to 12.0, and more preferably within therange from 11.0 to 12.0, at a liquid temperature of 25° C. as thereference temperature. The pH value may be adjusted by stopping thesupply of the alkaline aqueous solution into the agitation tank, orsupplying an inorganic acid having the metal of metal salt replaced withhydrogen (e.g., sulfuric acid in the case where the metal salt is asulfate) into the agitation tank, for example.

After adjusting the pH value, the ammonia concentration, thetemperature, and the like of the reaction aqueous solution, the rawmaterial liquid is supplied into the agitation tank while agitating thereaction aqueous solution. In this way, the nuclei may start growing(particle growth) through neutralization crystallization, and theparticle growth step S12 may be started. Note that although thenucleation step S11 and the particle growth step S12 are carried out inthe same agitation tank in the present embodiment, the above steps mayalso be performed in different agitation tanks.

In the particle growth step S12, when the pH value of the reactionaqueous solution is less than or equal to 12.0 and is lower than the pHvalue of the reaction aqueous solution during the nucleation step S11,new nuclei are hardly generated and particle growth takes precedenceover nucleation.

Note that when the pH value of the reaction aqueous solution is 12.0,the reaction aqueous solution is at a boundary condition betweennucleation and particle growth, and as such, whether nucleation orparticle growth will take precedence depends on the presence or absenceof nuclei in the reaction aqueous solution. For example, when the pHvalue of the reaction aqueous solution during the nucleation step S11 isadjusted to be higher than 12.0 to promote the generation of a largeamount nuclei, and the pH value of the reaction aqueous solution isthereafter adjusted to 12.0 for the particle growth step S12, particlegrowth will take precedence because a large amount of nuclei are presentin the reaction aqueous solution. On the other hand, when nuclei are notpresent in the aqueous reaction solution, i.e., when the pH value of thereaction aqueous solution during the nucleation step S11 is adjusted to12.0, nucleation will take precedence because there are no nuclei to begrown. Thereafter, when the pH value of the reaction aqueous solution isadjusted to be less than 12.0 for the particle growth step S12, thegenerated nuclei may be grown. In order to clearly separate nucleationand particle growth, the pH value in the particle growth step ispreferably adjusted to be lower than the pH value in the nucleation stepby a difference of at least 0.5, and more preferably by a difference ofat least 1.0.

Also, when the pH value of the reaction aqueous solution is greater thanor equal to 10.5 in the particle growth step S12, metal ions remainingin the solution without precipitation may be reduced owing to their lowsolubility in ammonium, and production efficiency may be improved.

In the particle growth step S12, an alkaline aqueous solution and anammonia aqueous solution are supplied into the agitation tank inaddition to the raw material liquid so that the pH value, the ammoniaconcentration, and the temperature of the reaction aqueous solution maybe maintained within the above ranges. In this way, particle growth maybe continued in the reaction aqueous solution.

The particle growth step S12 can be divided into a first half and asecond half by switching the atmosphere in the agitation tank. In thefirst half of the particle growth step, the atmosphere is an oxidizingatmosphere similar to that in the nucleation step S11. The oxygenconcentration in the oxidizing atmosphere is greater than or equal to 1vol %, more preferably greater than or equal to 2 vol %, and morepreferably greater than or equal to 10 vol %. The oxidizing atmospheremay be an ambient air atmosphere (oxygen concentration: 21 vol %), whichis easy to control, for example. The upper limit of the oxygenconcentration of the oxidizing atmosphere is not particularly limitedbut may be less than or equal to 30 vol %, for example. On the otherhand, in the second half of the particle growth step, the atmosphere isswitched to a non-oxidizing atmosphere. The oxygen concentration in thenon-oxidizing atmosphere is less than or equal to 1 vol %, morepreferably less than or equal to 0.5 vol %, and more preferably lessthan or equal to 0.3 vol %. The oxygen concentration in thenon-oxidizing atmosphere may be controlled by mixing oxygen gas orambient air and an inert gas, for example.

FIG. 2 is a schematic cross-sectional view of an aggregate formed in thefirst half of the particle growth step according to an embodiment of thepresent invention. FIG. 3 is a schematic cross-sectional view of anouter shell formed in the second half of the particle growth stepaccording to an embodiment of the present invention.

In the first half of the particle growth step S12, seed crystalparticles 2 are formed by promoting growth of nuclei, and as the seedcrystal particles 2 increase in size, the seed crystal particles 2 startto collide with each other to form an aggregate 4 made up of a pluralityof the seed crystal particles 2. On the other hand, in the second halfof the particle growth step S12, a fine outer shell 6 is formed aroundthe aggregate 4. As a result, particles each made up of the aggregate 4and the outer shell 6 are obtained.

Note that the structure of the nickel-containing hydroxide particle isnot limited to the structure shown in FIG. 3. For example, when thenucleation step S11 and the particle growth step S12 are performed atthe same time, the particle structure obtained upon completion ofneutralization crystallization may be a different structure from theparticle structure shown in FIG. 3. For example, structurescorresponding to the seed crystal particles 2 and structurescorresponding to the outer shells 6 may be merged and lessdistinguishable such that a more undifferentiated structure may beobtained.

The particle growth step S12 is ended at the time the nickel-containinghydroxide particles have grown to a predetermined particle diameter. Theparticle diameter of the nickel-containing hydroxide particles may beestimated based on the amount of metal salt supplied in the nucleationstep S11 and the particle growth step S12.

Note that after the nucleation step S11 and during the particle growthstep S12, the supply of the raw material liquid may be stopped and theagitation of the reaction aqueous solution may be stopped to cause theparticles to settle and to discharge the supernatant liquid above thesettled particles. In this way, the metal ion concentration in thereaction aqueous solution may be increased after the metal ionconcentration has decreased by neutralization crystallization.

FIG. 4 is a top view of a chemical reaction apparatus 10 that is used toimplement the method for producing a nickel-containing hydroxideaccording to an embodiment of the present invention. FIG. 5 is across-sectional view of the chemical reaction apparatus across line V-Vof FIG. 4.

The chemical reaction apparatus 10 includes an agitation tank 20, animpeller 30, a shaft 40, and a baffle 50. The agitation tank 20accommodates a reaction aqueous solution in a cylindrical inner space.The impeller 30 agitates the aqueous reaction solution in the agitationtank 20. The impeller 30 is attached to the lower end of the shaft 40.The impeller 30 may be rotated by rotating the shaft 40 with a motor orthe like. The center line of the agitation tank 20, the center line ofthe impeller 30, and the center line of the shaft 40 may coincide andmay be vertical. The baffle 50 is also referred to as a baffle plate.The baffle 50 protrudes from the inner peripheral surface of theagitation tank 20, and generates an upward flow and a downward flow byinterfering with a rotating flow, thereby improving agitation efficiencyof the reaction aqueous solution.

Also, the chemical reaction apparatus 10 includes a raw material liquidsupply pipe 60, an alkaline aqueous solution supply pipe 62, and anammonia water supply pipe 64. The raw material liquid supply pipe 60supplies the raw material liquid into the agitation tank 20. Thealkaline aqueous solution supply pipe 62 supplies an alkaline aqueoussolution into the agitation tank 20. The ammonia water supply pipe 64supplies ammonia water into the agitation tank 20.

The inventors of the present invention have investigated the conditionfor universally preventing sphericity degradation of particles obtainedat the completion of neutralization crystallization in various chemicalreaction apparatuses with various structures and have directed theirfocus on the acceleration of the reaction aqueous solution in theagitation tank 20 during the particle growth step S12.

FIG. 6 is a diagram showing a circular horizontal plane arrangeddirectly above the impeller and streamlines passing through thehorizontal plane according to an embodiment of the present invention.Note that the arrows in FIG. 6 represent velocity vectors of thestreamlines. Note that the velocity vectors of the streamlines alsoinclude components in the direction perpendicular to the drawingsurface.

In the particle growth step S12, particles are dispersed throughout thereaction aqueous solution, and the particles move along streamlinespassing through a circular horizontal plane 32 arranged directly abovethe impeller 30 and repeatedly pass through the horizontal plane 32. Thehorizontal plane 32 has a center coinciding with the center line of theimpeller 30 and has the same diameter as the diameter of the impeller30. The particles are accelerated and are applied a force by passingthrough the impeller 30.

When an averaged value obtained by averaging the maximum accelerations(>0) of the flows of the streamlines (hereinafter referred to as“average maximum acceleration of the flow”) is greater than 600 m/s²,bonding of the spherically grown particles can be prevented. Such aneffect may be attributed to the force applied to the acceleratedparticles overcoming the bonding force. The average maximum accelerationof the flow is calculated by obtaining the maximum value of theacceleration of each streamline and averaging the obtained maximumvalues.

In terms of preventing sphericity degradation of the particles obtainedat the completion of neutralization crystallization, the greater theaverage maximum acceleration of the flow, the greater the effect ofpreventing sphericity degradation. In this respect, the average maximumacceleration of the flow is preferably greater than or equal to 700m/s², more preferably greater than or equal to 1000 m/s², and morepreferably greater than or equal to 1200 m/s². However, in view ofconstraints on the capacity of the rotating motor for rotating theimpeller 30 and the like, the average maximum acceleration of the flowis preferably less than or equal to 7500 m/s².

Note that in the first half of the particle growth step S12, bycontrolling the average maximum acceleration of the flow, the particlediameter of the aggregates 4 may be controlled as well. That is, thegreater the average maximum acceleration of the flow, the smaller theparticle diameter of the aggregates 4.

The average maximum acceleration of the flow can be obtained bysimulation using general-purpose fluid analysis software. In thesimulation, the surface density of streamlines passing through thehorizontal plane 32 is set to at least 3000 lines/m². By setting thesurface density of the streamlines to at least 3000 lines/m², highlyreliable data can be obtained.

In the following, an example steady state fluid analysis in the case ofproducing nickel hydroxide by reacting nickel sulfate and sodiumhydroxide in a continuous agitation tank will be mainly described. Notethat the fluid analysis software used in the following example is ANSYSCFX Ver 15.0 (product name) manufactured by ANSYS Co., Ltd. The analysisconditions and the like are described below.

<Coordinate System>

-   -   A region around the shaft and the impeller from among the        regions to be analyzed in the fluid analysis (hereinafter also        referred to as “analysis region”) is covered by a rotating        coordinate system that rotates along with the shaft and the        impeller. The region to be covered by the rotating coordinate        system is cylindrical, its center line is arranged to coincide        with the center lines of the shaft and the impeller, its        diameter is set to 115% of the diameter of the impeller, and its        range in the vertical direction extends from the inner bottom        surface to the liquid surface of the agitation tank.    -   Other regions of the analysis region are covered by a stationary        coordinate system.    -   The rotating coordinate system and the stationary coordinate        system are connected using an interface function of the fluid        analysis software. Note that the optional setting “Frozen Rotor”        is used as the interface function of the fluid analysis        software.

<Turbulence Model>

-   -   The flow in the agitation tank is a turbulent flow rather than a        laminar flow. Specifically, the SST (Shear Stress Transport)        turbulence model is used as the turbulence model of the flow.

<Chemical Reaction>

-   -   The chemical reaction that occurs in the agitation tank may be        represented by the following formula:        NiSO₄+2NaOH→Ni(OH)₂+Na₂SO₄    -   In the fluid analysis, a single-phase multi-component fluid that        contains the following five components is analyzed.        1) Reactant component A: NiSO₄        2) Reactant component B: NaOH        3) Product component C: Ni(OH)₂        4) Product component D: Na₂SO₄        5) Water    -   The rate of the chemical reaction is calculated by the eddy        dissipation model. The eddy dissipation model is a reaction        model that assumes that the above chemical reaction occurs when        the reactant component A and the reactant component B are mixed        to the molecular level by turbulence dispersion. The settings of        the eddy dissipation model are left as is to the default        settings of the fluid analysis software.

<Calculation of Mass Fraction of Each Component>

-   -   The total mass fraction of the above five components at a given        time point and a given position in the analysis region is equal        to one. As such, the mass fraction of each of the four        components other than water from among the above five components        is obtained by solving the transport equation by CFX, and the        mass fraction of water is obtained by subtracting the total mass        fraction of the above four components from one.

<Boundary Condition>

Wall Boundary (Boundary with No Fluid Flow)

It is assumed that no slip occurs at boundaries with solid surfaces suchas the agitation tank, the shaft, the impeller, the baffle, and thelike. On the other hand, it is assumed that slips occur at the boundarywith the outside air (liquid surface). Note that that the liquid surfaceis assumed to be a flat surface with a constant height that is notdeformed by agitation.

Inflow Boundary (Boundary where Fluid Enters)

An inflow boundary where an aqueous solution containing the reactantcomponent A (hereinafter referred to as “aqueous solution A”) flows intothe fluid in the agitation tank and an inflow boundary where an aqueoussolution containing the reactant component B (hereinafter referred to as“aqueous solution B”) flows into the fluid in the agitation tank areseparately provided.

It is assumed that the inflow rate of the aqueous solution A, theproportion of the reactant component A in the aqueous solution A, theinflow rate of the aqueous solution B, and the proportion of thereactant component B in the aqueous solution B are constant. The inflowrate of the aqueous solution B is set up so that the pH value of theaqueous solution in the agitation tank is maintained at a predeterminedvalue (e.g., 12.0).

Outflow Boundary (Boundary where Fluid Flows Out)

An outflow boundary where the fluid in the agitation tank flows out isprovided on a part of the inner peripheral surface of the agitationtank. The outflowing liquid contains the product components C and D, theunreacted reactant components A and B, and water. The outflow rate ofthe outflowing liquid is set up so that the pressure difference betweenthe analysis region and a region outside the system becomes zero.

Note that in a case where an overflow type continuous system is used,the liquid surface corresponds to the outflow boundary.

<Thermal Condition>

-   -   The temperature of the fluid in the agitation tank is maintained        constant at 25° C. It is assumed that heat generation by the        chemical reaction and heat input/output at the inflow boundary        and the outflow boundary do not occur.

<Initial Condition>

-   -   The fluid in the agitation tank, in its initial state, is        assumed to be homogeneous and contains only two components out        of the above five components, i.e., the reactant component B and        water. Specifically, the initial mass fraction of the reactant        component A, the initial mass fraction of the product component        C, the initial mass fraction of the product component D in the        fluid in the agitation tank at the initial stage are zero, and        the initial mass fraction of the reactant component B is set up        so that the pH value of the aqueous solution in the agitation        tank will be at the above predetermined value.

Note that although the initial mass fraction of the product component Cand the initial mass fraction of the product component D are set to zeroin the present example, in order to reduce the number of iterativecalculations (i.e., calculation time) for obtaining a steady statesolution, the initial mass fraction may alternatively be set to theaverage value for the entire analysis region that is estimated to bereached in a steady state, for example. The average value for the entireanalysis region may be calculated based on the inflow rate of theaqueous solution A, the proportion of the reactant component A in theaqueous solution A, the inflow rate of the aqueous solution B, theproportion of the reactant component B in the aqueous solution B, thequantitative relationship expressed by the chemical reaction formula,and the like.

<Convergence Determination>

-   -   The iterative calculations for obtaining a steady state solution        are performed until the root mean square errors of the flow        velocity component (m/s) of the flow, the pressure (Pa), and the        mass fractions of the above four components at a given position        in the analysis region become less than or equal to 10⁻⁴.

Note that although analysis conditions for obtaining a nickel hydroxideare described above-described analysis conditions for obtaining a nickelcomposite hydroxide can be similarly set up. For example, in the case ofobtaining a nickel-manganese composite hydroxide by reacting nickelsulfate and manganese sulfate with sodium hydroxide, the fluid analysisinvolves analyzing a single-phase multi-component fluid that containsthe following seven components.

1) Reactant component A1: NiSO₄

2) Reactant component A2: MnSO₄

3) Reactant component B: NaOH

4) Product component C1: Ni(OH)₂

5) Product component C2: Mn(OH)₂

6) Product component D: Na₂SO₄

7) Water

In the above example, it is assumed that two chemical reactions, i.e.,“A1+2B→C1+D” and “A2+2B→C2+D” occur in the agitation tank, and an eddydissipation model corresponding to each chemical reaction is used as areaction model. The reactant component A1 and the reactant component A2are uniformly dissolved in water and supplied from the same inflowboundary. That is, an aqueous solution A containing both the reactantcomponent A1 and the reactant component A2 is supplied from the inflowboundary.

Also, for example, in the case of obtaining a nickel composite hydroxidethat contains nickel, cobalt, and aluminum using nickel sulfate, cobaltsulfate, and aluminum sulfate, the fluid analysis involves analyzing asingle-phase multi-component fluid that contains the following ninecomponents.

1) Reactant component A1: NiSO₄

2) Reactant component A2: CoSO₄

3) Reactant component A3: A1₂(SO₄)₃

4) Reactant component B: NaOH

5) Product component C1: Ni(OH)₂

6) Product component C2: Co(OH)₂

7) Product component C3: A1(OH)₃

8) Product component D: Na₂SO₄

9) Water

In the above example, it is assumed that three chemical reactions, i.e.,“A1+2B→C1+D”, “A2+2B→C2+D”, and “1/2A3+3B→C3+3/2D” occur in theagitation tank, and an eddy dissipation model corresponding to eachchemical reaction is used as a reaction model. The reactant componentA1, the reactant component A2, and the reactant component A3 areuniformly dissolved in water and supplied from the same inflow boundary.That is, an aqueous solution A containing the reactant component A1, thereactant component A2, and the reactant component A3 is supplied fromthe inflow boundary.

Further, for example, in the case of obtaining a nickel-cobalt-manganesecomposite hydroxide using nickel sulfate, manganese sulfate, and cobaltsulfate, the fluid analysis involves analyzing a single-phasemulticomponent fluid that contains the following nine components.

1) Reactant component A1: NiSO₄

2) Reactant component A2: MnSO₄

3) Reactant component A3: CoSO₄

4) Reactant component B: NaOH

5) Product component C1: Ni(OH)₂

6) Product component C2: Mn(OH)₂

7) Product component C3: Co(OH)₂

8) Product Component D: Na₂SO₄

9) Water

In the above example, it is assumed that three chemical reactions, i.e.,“A1+2B→C1+D”, “A2+2B→C2+D”, and “1/2A3+3B→C3+3/2D” occur in theagitation tank, and an eddy dissipation model corresponding to eachchemical reaction is used as a reaction model. The reactant componentA1, the reactant component A2, and the reactant component A3 areuniformly dissolved in water and supplied from the same inflow boundary.That is, an aqueous solution A containing the reactant component A1, thereactant component A2, and the reactant component A3 is supplied fromthe inflow boundary.

Note that in some embodiments, more than one inflow boundaries for theaqueous solution A may be provided.

The method for producing a nickel-containing hydroxide may include astep of confirming by simulation that the average maximum accelerationof the flow of the streamlines for the aqueous solution in the agitationtank during the particle growth step is greater than 600 m/s². Such aconfirmation may be made each time a production condition is changed.Changing a production condition may include, for example, changing thecapacity or shape of the agitation tank; changing the number, shape,size, or installation location of the impeller; changing the rotationspeed of the impeller; changing the flow rate or concentration of theraw material liquid; or changing the shape, the number, or the locationof nozzles for supplying the raw material liquid. For example, in thecase of using a batch agitation tank, the confirmation may only need tobe made once under the same production conditions; that is, theconfirmation does not have to be made every time production is performedas long as the production conditions are not changed.

Note that the actual reaction aqueous solution also contains ammonia asa chemical component. However, ammonia is not directly involved in theprecipitation reaction of solid particles, and its concentration is alsolower than the concentration of nickel hydroxide. As such, it may bepresumed that the influence of ammonia on the volume of a highlysupersaturated region of nickel hydroxide is small. Thus, ammonia, asone of chemical components to be solved in the simulation model, istreated as water.

EXAMPLES Example 1

In Example 1, a nucleation step of generating nuclei of nickel compositehydroxide particles by neutralization crystallization and a particlegrowth step of promoting growth of the particles were carried out at thesame time using an overflow type continuous agitation tank.

The volume of the agitation tank was 5 L, a disk-blade turbine impellerwas used, the impeller had six blades, the diameter of the impeller was80 mm, the vertical distance between the impeller and the inner bottomsurface of the agitation tank was 5 mm, and the rotation speed of theimpeller was set to 850 rpm.

The agitation tank was filled with 5 L of the reaction aqueous solution,the pH value of the reaction aqueous solution was 11.3, the ammoniaconcentration of the reaction aqueous solution was 10 g/L, and thetemperature of the reaction aqueous solution was maintained at 50° C.The ambient atmosphere of the reaction aqueous solution was arranged tobe a nitrogen atmosphere.

The raw material liquid was prepared so that a nickel compositehydroxide with the formula Ni_(0.82)Co_(0.15)Al_(10.0)(OH)₂ could beobtained. One raw material liquid supply pipe was provided, and the feedrate of the raw material liquid supplied from the one raw materialliquid supply pipe was set to 400 mL/min.

During the nucleation step and the particle growth step, a sodiumhydroxide aqueous solution and ammonia water were supplied into theagitation tank in addition to the raw material liquid so as to maintainthe pH value of the reaction aqueous solution and the ammoniaconcentration of the reaction aqueous solution.

The average maximum acceleration of the flow, calculated by simulation,was 1395 m/s². Note that the analysis conditions were set up to be thesame as the above-described analysis conditions.

FIG. 7 shows an SEM image of nickel composite hydroxide particlesobtained in Example 1. As shown in FIG. 7, particles with highsphericity were obtained.

Example 2

In Example 2, nickel composite hydroxide particles were produced in thesame manner as in Example 1 except that the rotation speed of theimpeller was set to 600 rpm.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 720 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 3

In Example 3, nickel composite hydroxide particles were produced in thesame manner as in Example 1 except that the diameter of the impeller was60 mm and the rotation speed of the impeller was set to 1000 rpm.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 1040 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 4

In Example 4, nickel composite hydroxide particles were produced in thesame manner as in Example 1 except that a 45° pitched paddle bladeimpeller was used, the impeller had four blades, the diameter of theimpeller was 80 mm, the vertical distance between the impeller and theinner bottom surface of the agitation tank was 5 mm, and the rotationspeed of the impeller was set to 850 rpm.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 900 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 5

In Example 5, the volume of the agitation tank was 50 L, a blade-diskturbine impeller was used, the impeller had six blades, the diameter ofthe impeller was 160 mm, the vertical distance between the impeller andthe inner bottom surface of the agitation tank was 5 mm, and therotation speed of the impeller was set to 500 rpm. Further, the feedrate of the raw material liquid was set to 4000 mL/min. Aside from theabove-noted conditions, nickel composite hydroxide particles wereproduced in the same manner as in Example 1.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 1340 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 6

In Example 6, nickel composite hydroxide particles were produced in thesame manner as in Example 1 except that the raw material liquid wasprepared so that a nickel composite hydroxide with the formulaNi_(0.88)Co_(0.09)Al_(10.0)(OH)₂ could be obtained.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 1395 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 7

In Example 7, nickel composite hydroxide particles were produced in thesame manner as in Example 1 except that the raw material liquid wasprepared so that a nickel composite hydroxide with the formulaNi_(0.34)Co_(0.33)Mn_(0.33)(OH)₂ could be obtained.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 1395 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 8

In Example 8, nickel composite hydroxide particles were produced in thesame manner as in Example 1 except that the raw material liquid wasadjusted so that a nickel composite hydroxide with the formulaNi_(0.60)Co_(0.20)Mn_(0.20)(OH)₂ could be obtained.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 1395 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 9

In Example 9, a 45° pitched paddle blade impeller was used, the impellerhad four blades, the diameter of the impeller was 80 mm, the verticaldistance between the impeller and the inner bottom surface of theagitation tank was 5 mm, and the rotation speed of the impeller was setto 850 rpm. The composition of the raw material liquid was adjusted sothat a nickel composite hydroxide with the formulaNi_(0.34)CO_(0.33)Mn_(0.33)(OH)₂ could be obtained. Aside from theabove-noted conditions, nickel composite hydroxide particles wereproduced in the same manner as in Example 1.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 900 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Example 10

In Example 10, the volume of the agitation tank was 50 L, a disk-bladeturbine impeller was used, the impeller had six blades, the diameter ofthe impeller was 160 mm, the vertical distance between the impeller andthe inner bottom surface of the agitation tank was 5 mm, and therotation speed of the impeller was set to 500 rpm. Further, the feedrate of the raw material liquid was set to 4000 mL/min. The compositionof the raw material liquid was adjusted so that a nickel compositehydroxide with the formula Ni_(0.34)Co_(0.33)Mn_(0.33)(OH)₂ could beobtained. Aside from the above-noted conditions, nickel compositehydroxide particles were produced in the same manner as in Example 1.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 1340 m/s². The analysisconditions were set up to be the same as the above-described analysisconditions.

An SEM image of the obtained nickel composite hydroxide particles wassimilar to that of the nickel composite hydroxide particles obtained inExample 1 and particles with high sphericity were obtained.

Comparative Example 1

In Comparative Example 1, nickel composite hydroxide particles wereproduced in the same manner as in Example 1 except that the rotationspeed of the impeller was set to 500 rpm.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 600 m/s².

FIG. 8 shows an SEM image of the nickel composite hydroxide particlesobtained in Comparative Example 1. As can be appreciated from theparticles encircled by bold lines in FIG. 8, particles with lowsphericity were observed from the particles obtained in ComparativeExample 1.

Comparative Example 2

In Comparative Example 2, the rotation speed of the impeller was set to500 rpm. The composition of the raw material liquid was adjusted so thata nickel composite hydroxide with the formulaNi_(0.34)Co_(0.33)Mn_(0.33)(OH)₂ could be obtained. Aside from theabove-noted conditions, nickel composite hydroxide particles wereproduced in the same manner as in Example 1.

The average maximum acceleration of the flow, calculated by simulationin the same manner as in Example 1, was 600 m/s².

An SEM image of the nickel composite hydroxide particles obtained inComparative Example 2 was substantially similar to the particlesobtained in Comparative Example 1 and particles with low sphericity wereobserved.

SUMMARY

As can be appreciated from Examples 1 to 10 and Comparative Examples 1and 2, as long as the average maximum acceleration of the flow isgreater than 600 m/s², sphericity degradation of particles obtained atthe completion of neutralization crystallization can be prevented evenif the type of impeller, the diameter of the impeller, and the volume ofthe agitation tank are changed.

Although the method for producing a nickel-containing hydroxideaccording to the present invention have been described above withrespect to illustrative embodiments, the present invention is notlimited to the above-described embodiments and various modifications andimprovements may be made within the scope of the present invention.

The present application claims priority to Japanese Patent ApplicationNo. 2016-118367 filed on Jun. 14, 2016, the entire contents of which areherein incorporated by reference.

DESCRIPTION OF THE REFERENCE NUMERALS

-   2 seed crystal particle-   4 aggregate-   6 outer shell-   10 chemical reaction apparatus-   20 agitation tank-   30 impeller-   32 horizontal plane-   40 shaft-   50 baffle-   60 raw material liquid supply pipe-   62 alkaline aqueous solution supply pipe-   64 ammonia water supply pipe

The invention claimed is:
 1. A method for producing a nickel-containinghydroxide, the method comprising: a particle growth step of promotinggrowth of nickel-containing hydroxide particles by neutralizationcrystallization in an aqueous solution accommodated in an agitationtank; wherein in the particle growth step, an averaged value of maximumaccelerations of flows of streamlines for the aqueous solution isgreater than 600 m/s².
 2. The method for producing a nickel-containinghydroxide according to claim 1, wherein the nickel-containing hydroxideis produced so as to contain Ni, Co, and Al at an amount ratio ofNi:Co:Al=(1-x-y):x:y, where 0≤x≤0.3 and 0.005≤y≤0.15.
 3. The method forproducing a nickel-containing hydroxide according to claim 1, whereinthe nickel-containing hydroxide is produced so as to contain Ni, Co, Mn,and M, where M denotes at least one additional element selected from agroup consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, at an amountratio of Ni:Co:Mn:M=x:y:z:t, where x+y+z+t=1, 0.1≤x≤0.7, 0.1≤y≤0.5,0.1≤z≤0.8, and 0≤t≤0.02.